JP4134614B2 - Optical transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmitter capable of keeping the wavelength of output light constant.
[0002]
[Prior art]
Although the wavelength output from the semiconductor laser changes depending on the temperature of the chip on which the semiconductor laser is formed, an optical transmitter that can keep the output wavelength constant is conventionally known.
[0003]
FIG. 3 is a block diagram showing a configuration of a conventional optical transmitter. In the conventional optical transmitter 3, the backward monitoring light of the semiconductor laser (LD) 31 is collimated by the collimator lens (CL) 33, and then branched by the splitter (ST) 34. The light is received by the first photodiode 36 for monitoring, and the other branched light is transmitted through the etalon 35 having variable wavelength and then received by the second photodiode 37 for monitoring. Based on the amount of light received by the first photodiode 36, the automatic power control unit (APC) 38 transmits a signal to the semiconductor laser driver (DRV) 32 to control the power of the semiconductor laser 31, and the second photo Based on the amount of light received by the diode 37, the automatic temperature control unit (ATC) 39 transmits a signal to the temperature control element 40 to control the temperature of the chip of the semiconductor laser 31, whereby the wavelength of light output from the semiconductor laser 31 Was controlling.
[0004]
[Problems to be solved by the invention]
However, the optical transmitter 3 described above includes two monitoring photodiodes 36 and 37, and the arrangement of components is complicated to allow light to enter the photodiodes 36 and 37. There was a problem that the space that constitutes would widen. There is also a problem that the number of parts constituting the optical transmitter 3 is large.
[0005]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide an optical transmitter that is reduced in size by reducing the number of components and making the arrangement of components more efficient.
[0006]
[Means for Solving the Problems]
An optical transmitter according to the present invention outputs a semiconductor laser, an electroabsorption optical modulator monolithically mounted on a chip on which the semiconductor laser is formed, and the semiconductor laser passing through the electroabsorption optical modulator. A photodiode that is arranged on the optical axis of light and outputs a signal corresponding to the amount of received light, a power control unit that is connected to the photodiode and controls the power of the semiconductor laser, and is connected to the photodiode and connected to the chip A temperature control unit for controlling the temperature, a first mode in which a voltage applied to the electroabsorption optical modulator is changed to transmit all the light output from the semiconductor laser, and a part of the light output from the semiconductor laser An optical modulator controller that switches between the second mode and the power controller. The power controller controls the electroabsorption optical modulator to the first mode by the optical modulator controller. The temperature control unit is controlled by the optical modulator control unit so that the power of the light output from the semiconductor laser is constant based on the signal output from the photodiode. The temperature of the chip is controlled so that the wavelength of light output from the semiconductor laser is constant based on a signal output from the photodiode when the is in the second mode.
[0007]
In this manner, a photodiode is disposed on the optical axis of the light output from the semiconductor laser through the electroabsorption optical modulator. Then, by changing the voltage applied to the electroabsorption optical modulator, all of the light from the semiconductor laser is transmitted and incident on the photodiode, and part of the light from the semiconductor laser is transmitted. To switch to the second mode to be incident on the photodiode. “Transmit part of the light output from the semiconductor laser” means that light that passes through by shifting the absorption edge wavelength of the electroabsorption optical modulator to include the wavelength of the light output from the semiconductor laser. Means a state of absorbing a part of At the absorption edge wavelength, the transmittance (absorption rate) of light passing through the electroabsorption optical modulator changes as the wavelength changes, so that the wavelength of light can be calculated from the transmittance. . That is, in the second mode, the wavelength of light output from the semiconductor laser can be monitored by the amount of light received by the photodiode. In the first mode, the power of light output from the semiconductor laser can be monitored by the amount of light received by the photodiode. Therefore, power control by the power control unit and temperature control by the temperature control unit can be performed based on the signal output from the photodiode in each mode. By adopting such a configuration, a single monitoring photodiode can be used, and the number of parts can be reduced. Further, since the output light from the semiconductor laser has only to be incident on one photodiode, the arrangement of the components can be simplified, and the optical transmitter can be miniaturized. Further, since the electroabsorption optical modulator is monolithically mounted on the semiconductor laser chip, the size can be further reduced.
[0008]
In the above optical transmitter, the semiconductor laser can output a plurality of light beams having a predetermined wavelength depending on the setting, and an electroabsorption type optical modulator is used in order to set the electroabsorption optical modulator to the first mode and the second mode. The memory further stores information on the voltage applied to the optical modulator for each predetermined wavelength, and the optical modulator controller applies the voltage to the electroabsorption optical modulator based on the information stored in the memory. It may be characterized by.
[0009]
When the semiconductor laser is capable of outputting a plurality of light beams having a predetermined wavelength, an applied voltage for setting the first mode for transmitting all the output light from the semiconductor laser for each predetermined wavelength, and an output By storing in the memory the information on the applied voltage for setting the second mode that transmits a part of the light, the voltage corresponding to each predetermined wavelength is referred to by referring to the information stored in the memory. Control to switch between the first mode and the second mode by applying to the electroabsorption optical modulator can be performed.
[0010]
The optical transmitter is monolithically mounted in the vicinity of the semiconductor laser that outputs signal light from the first end face and the second end face opposite to the first end face of the chip on which the semiconductor laser is formed. and electroabsorption modulator was disposed on the optical axis of the light output from the second end surface, and a photodiode that outputs a signal corresponding to the amount of received light, may be provided.
[0011]
The electroabsorption optical modulator is monolithically mounted on the second end surface side opposite to the first end surface from which the signal light is output on the chip on which the semiconductor laser is formed, and the electroabsorption type If a configuration is employed in which a photodiode is arranged on the optical axis of the light that passes through the optical modulator and is output from the second end face, the second light in which all the light from the semiconductor laser is transmitted by the electroabsorption optical modulator. The output light from the end face of the semiconductor laser can be received by the photodiode, and the power of the signal light output from the first end face of the semiconductor laser can be monitored. The light from the semiconductor laser can be monitored by the electroabsorption optical modulator. The output light from the second end face that is partially transmitted can be received by the photodiode, and the wavelength of the signal light output from the first end face of the semiconductor laser can be monitored.
[0012]
Optical transceiver may be provided with the optical transmitter.
[0013]
An optical transmitter / receiver including the above-described optical transmitter is preferable because the power and wavelength of the output light can be adjusted to be kept constant.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of an optical transmitter according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
[0015]
FIG. 1 is a block diagram showing a configuration of an optical transmitter 1 according to an embodiment of the present invention. As shown in FIG. 1, an optical transmitter 1 includes a semiconductor laser (LD) 11, a semiconductor laser driver (DRV) 13, an electroabsorption optical modulator (hereinafter simply referred to as “optical modulator”) 12, An optical modulator control unit (EA CTRL) 15, a monitoring photodiode (mPD) 14, a switch (SW) 21, an automatic power control unit (APC) 16, and an automatic temperature control unit (ATC) 17 , TEC 18, CPU 19, and memory 20.
[0016]
The semiconductor laser 11 and the optical modulator 12 are monolithically formed on one chip 10. That is, a so-called modulator integrated semiconductor laser is used here. The semiconductor laser 11 outputs signal light from one end face of the chip 10 (referred to as “first end face 10A”), and from the end face opposite to the first end face 10A (referred to as “second end face 10B”), The monitoring light that has passed through the optical modulator 12 is output.
[0017]
The optical modulator control unit 15 is connected to the optical modulator 12, and has a function of shifting the wavelength of light absorbed by the optical modulator 12 by changing a voltage applied to the optical modulator 12.
[0018]
The semiconductor laser driver 13 is connected to the semiconductor laser 11 and has a function of driving the semiconductor laser 11 based on inputted data.
[0019]
The photodiode 14 is disposed to face the second end face 10B of the chip on which the semiconductor laser 11 is formed, and receives a light output from the second end face 10B and outputs a signal corresponding to the amount of light received. Have
[0020]
The automatic power control unit 16 has a function of controlling the semiconductor laser driver 13 based on a signal from the photodiode 14 and controlling the power of the signal light output from the semiconductor laser 11 to be constant.
[0021]
The automatic temperature control unit 17 has a function of controlling the TEC 18 based on a signal from the photodiode 14 and controlling the wavelength of the signal light output from the semiconductor laser 11 to be constant. The TEC 18 is a temperature control device such as a Peltier element, and the chip 10 and the photodiode 14 are mounted on the TEC 18.
[0022]
A switch 21 is disposed between the photodiode 14, the automatic power control unit 16, and the automatic temperature control unit 17. The switch 21 is connected to the first terminal 21 ₁ connected to the output of the photodiode 14, the second terminal 21 ₂ connected to the input of the automatic power control unit 16, and the first terminal connected to the input of the automatic temperature control unit 17. 3 terminal 21 ₃ , and has a function of passing a signal either between the first terminal 21 ₁ and the second terminal 21 ₂ or between the first terminal 21 ₁ and the third terminal 21 _3. . The switch 21 is connected to the CPU 19, and the switch control of the switch 21 is performed by the CPU 19.
[0023]
The CPU 19 has a function of transmitting an instruction to the optical modulator control unit 15 and the switch 21 and controlling the optical modulator control unit 15 and the switch 21 in synchronization. That is, when the control in the first mode is performed, the CPU 19 sends a command to the light modulation control unit 15 to control the voltage applied to the light modulator 12 so that all of the output light from the semiconductor laser 11 is light modulated. The CPU 19 allows the signal to pass between the first terminal 21 ₁ and the second terminal 21 ₂ and allows the signal output from the photodiode 14 to be input to the automatic power control unit 16. Conversely, when performing control in the second mode, the CPU 19 sends a command to the light modulation control unit 15 to control the voltage applied to the light modulator 12 so that part of the output light from the semiconductor laser 11 is generated. While allowing the light to pass through the optical modulator 12, the CPU 19 passes the signal between the first terminal 21 ₁ and the third terminal 21 ₃ and inputs the signal output from the photodiode 14 to the automatic temperature control unit 17. Let
[0024]
The memory 20 connected to the CPU 19 has a function of storing information on a voltage value applied to the optical modulator 12 in order to switch the optical modulator 12 between the first mode and the second mode. FIG. 2 is a diagram showing the relationship between the wavelength passing through the optical modulator 12 and the output from the photodiode 14 when the applied voltage V _EA is high (H) and low (L). As shown in FIG. 2, when the voltage applied to the optical modulator 12 is increased, the wavelength transmitted through the optical modulator 12 is shifted to the larger side. The voltage value (H) for setting the optical modulator 12 to the first mode is a voltage value such that the absorption edge wavelength of the optical modulator 12 is larger than the target wavelength λa of the output light from the semiconductor laser 11. is there. Thereby, all the light of wavelength λa output from the semiconductor laser 11 passes through the optical modulator 12. The voltage value (L) for setting the optical modulator 12 to the second mode is such that the absorption wavelength of the optical modulator 12 includes the target wavelength λa of the output light from the semiconductor laser 11. It is. The memory 20 stores these voltage values _VEA . When the semiconductor laser 11 has a plurality of target wavelengths λa by setting and can switch between them, a plurality of voltage values H and voltage values L are stored according to respective predetermined wavelengths that can be output from the semiconductor laser 11. .
[0025]
Next, the operation of the optical transmitter 1 according to this embodiment will be described.
[0026]
First, when data is input to the semiconductor laser driver 13, the semiconductor laser driver 13 drives the semiconductor laser 11 to output signal light based on the input data from the first end face 10 </ b> A of the chip 10. The semiconductor laser 11 outputs light in the direction opposite to the first end face 10A, and the light that has passed through the optical modulator 12 is output from the second end face 10B of the chip 10. The light output from the second end face 10 </ b> B is input to the photodiode 14. The CPU 19 controls the optical modulator control unit 15, and the optical modulator control unit 15 applies the voltage H to the optical modulator 12 to place the optical modulator 12 in the first mode. Thereby, all the light output from the semiconductor laser 11 passes through the optical modulator 12 and is input to the photodiode 14. Further, the CPU 19 controls the switch 21 to pass a signal between the first terminal 21 ₁ and the second terminal 21 ₂ . Thereby, the signal output from the photodiode 14 is input to the automatic power control unit 16. In this case, since all the light output from the semiconductor laser 11 is received by the photodiode 14, the signal from the photodiode 14 is proportional to the power of the output light from the semiconductor laser 11. The automatic power control unit 16 transmits a command to the semiconductor laser driver 13 based on the signal from the photodiode 14 and controls the power of the output light of the semiconductor laser 11.
[0027]
Next, the CPU 19 controls the optical modulator control unit 15, and the optical modulator control unit 15 applies the voltage L to the optical modulator 12 to place the optical modulator 12 in the second mode. Thereby, a part of the light output from the semiconductor laser 11 is absorbed by the optical modulator 12, and part of the light is transmitted to the photodiode 14. Further, the CPU 19 controls the switch 21 to pass a signal between the first terminal 21 ₁ and the third terminal 21 ₃ . Thereby, the signal output from the photodiode 14 is input to the automatic temperature control unit 17. The automatic temperature control unit 17 transmits a command to the TEC 18 based on the signal from the photodiode 14 and controls the wavelength of the output light of the semiconductor laser 11. This control will be described in detail. As shown in FIG. 2, in the second mode, the absorption edge wavelength of the optical modulator 12 is controlled to include the target wavelength λa. When the wavelength of the output light from the semiconductor laser 11 changes from the wavelength λa, the amount of light transmitted through the optical modulator 12 changes. Specifically, the transmittance decreases when the wavelength shifts to the larger side, and the transmittance increases when the wavelength shifts to the smaller side. Therefore, information on the wavelength of the output light from the semiconductor laser 11 can be obtained based on the signal from the photodiode 14. The automatic temperature controller 17 controls the wavelength of the output light to be constant based on the signal from the photodiode 14.
[0028]
The optical transmitter 1 according to this embodiment includes a modulator integrated semiconductor laser in which a semiconductor laser 11 and an optical modulator 12 are monolithically integrated, and a photodiode that receives light output through the optical modulator 12. 14, and by changing the transmittance of the output light from the semiconductor laser 11 by the optical modulator 12, it is possible to monitor both the power and the wavelength of the output light of the semiconductor laser 11 by one photodiode 14. . Thereby, arrangement | positioning of the photodiode 14 which receives the output light from the semiconductor laser 11 can be made simple, and the optical transmitter 1 can be comprised in a narrow space. In addition, the number of parts constituting the optical transmitter 1 can be reduced.
[0029]
While the present invention has been described in detail with reference to the embodiment, the present invention is not limited to the above embodiment.
[0030]
The optical transmitter 1 of the present invention can be applied to the optical transmitter 1 capable of outputting a plurality of lights having a predetermined wavelength. In this case, the voltage value (H) applied to the optical modulator 12 for each predetermined wavelength. ) And voltage value (L) information is stored in the memory 20, and the CPU 19 transmits a command to the optical modulator control unit 15 based on the output wavelength.
[0031]
In the above embodiment, the optical transmitter 1 has been described as an example. However, the present invention may be applied to an optical transceiver.
[0032]
【The invention's effect】
According to the present invention, a photodiode is disposed on the optical axis of light output from a semiconductor laser through an electroabsorption optical modulator, and a voltage applied to the electroabsorption optical modulator is changed. The first mode in which all the light from the semiconductor laser is transmitted and incident on the photodiode is switched to the second mode in which a part of the light from the semiconductor laser is transmitted and incident on the photodiode. As a result, both the power and wavelength of the output light can be monitored and the power and wavelength can be controlled by one photodiode, so that the number of parts can be reduced. Further, since the output light from the semiconductor laser has only to be incident on one photodiode, the arrangement of the components can be simplified, and the optical transmitter can be miniaturized. The electroabsorption optical modulator can be further reduced in size by being monolithically mounted on a semiconductor laser chip.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an optical transmitter according to an embodiment.
FIG. 2 is a diagram illustrating a relationship between an absorption end of an optical modulator and an output from a photodiode.
FIG. 3 is a diagram illustrating a configuration of a conventional optical transmitter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical transmitter, 10 ... Chip, 11 ... Semiconductor laser, 12 ... Optical modulator, 13 ... Semiconductor laser driver, 14 ... Photodiode, 15 ... Optical modulator control part, 16 ... Automatic power control part, 17 ... Automatic Temperature control unit, 18 ... TEC, 19 ... CPU, 20 ... memory, 21 ... switch.

Claims (2)

A semiconductor laser;
An electroabsorption optical modulator monolithically mounted on a chip on which the semiconductor laser is formed;
A photodiode arranged on the optical axis of light output from the semiconductor laser through the electroabsorption optical modulator and outputting a signal corresponding to the amount of received light;
A power control unit connected to the photodiode and controlling the power of the semiconductor laser;
A temperature control unit connected to the photodiode and controlling the temperature of the chip;
A first mode in which a voltage applied to the electroabsorption optical modulator is changed to transmit all the light output from the semiconductor laser, and a second mode in which a part of the light output from the semiconductor laser is transmitted. An optical modulator controller that switches between modes,
With
The power control unit is configured to control a light output from the semiconductor laser based on a signal output from the photodiode when the electroabsorption optical modulator is set to the first mode by the optical modulator control unit. Control the power to be constant,
The temperature control unit is configured to control a light output from the semiconductor laser based on a signal output from the photodiode when the electroabsorption optical modulator is set to the second mode by the optical modulator control unit. Controlling the temperature of the chip so that the wavelength is constant,
An optical transmitter characterized by that. The semiconductor laser can output light of a plurality of predetermined wavelengths depending on settings,
A memory storing information about a voltage applied to the electroabsorption optical modulator for each of the predetermined wavelengths in order to set the electroabsorption optical modulator to the first mode and the second mode; Prepared,
The optical modulator control unit applies a voltage to the electroabsorption optical modulator based on information stored in the memory;
The optical transmitter according to claim 1.

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